This invention relates to an improved apparatus for holding a planar microscope slide during rapid rotation in preparation of a thin uniform monocellular layer sample or specimen on the surface of the slide and an improved system cooperating with the slide holder for handling the spin-off therefrom.
The use of a centrifuge or spinner to prepare a thin uniform layer of a liquid such as flood or a solution of plastic or of photoresist is well known. For example, U.S. Pat. No. 3,577,267 describes a method for preparing a monocellular layer of blood by means of such a spinner.
In the practice of making thin layer blood smears for clinical examination, it is important to make the process of inserting a clean slide into the spinner as simple as possible to conserve time and labor and to minimize handling of the slide before the sample is spun. This follows since any finger print or other hydrophobic deposits on the slide will interfere with the formation of a uniform sample layer. Additionally, the slide holder must be able to transmit rapid accelerations to the slide without chipping or damaging the slide. Also, the slide must be held positively and securely to eliminate fluttering or disengagement from the slide holder at high speeds causing breakage of the slide and a possible hazard to the operator.
Another important consideration in the design and configuration of a slide holder is the fact that spin-off of a liquid from a rotating surface disposed perpendicularly to the axis of rotation is a well-known method of producing an aerosol. This aerosol may be a cloud of liquid droplets ranging from large irregular masses to air-borne drops of 10 microns or less in diameter according to conditions of speed of rotation, viscosity and surface tension of the liquid, presence of projecting impact surfaces and other factors. Aerosols in the size range under 10 microns may be air-borne for a considerable length of time. If the droplets should contain a hazardous substance, a risk may exist to personnel in the laboratory where the spinner is in use.
A slide holder, therefore, should be designed to minimize the formation of such hazardous aerosols and, if possible, to cooperate in the trapping and suppression of the aerosol, if generated, by functioning within a system which can intercept and retain the aerosol as well as more massive spin-off.
Still another requirement for a slide holder is that it should have low rotational inertia to permit rapid acceleration and to minimize coasting time of the holder after the spin and sample preparation is completed.
U.S. Pat. No. 3,577,267 cited above suggests that a vacuum may be applied to the lower surface of the slide to hold the slide in position on the spinning support holder. The patent discloses the use of a vacuum pumping mechanism and because of the specific construction disclosed, a rather powerful motor is required to provide adequate acceleration to the sample. The present invention provides a construction which is simplified in comparison to the prior art yet which provides the advantages that follow from the use of a vacuum for holding a slide sample in position.